The present invention relates to a light amplifier.
Recent development of light amplifiers enables direct amplification of light signals, eliminating the need for providing electrooptical and optoelectrical converters at periodic intervals along an optical transmission medium. However, light amplification accompanies spontaneous emission which degrades the quality of a signal being transmitted. To overcome this problem, a prior art approach involves the use of an optical filter such as dielectric multilayered filter having a single narrow passband as described in a paper titled "Long-haul high-speed optical communication systems using a semiconductor laser amplifier", Shu Yamamoto et al, OFC'88, page 18.
One serious problem of the prior art light amplifier is that it cannot be used for amplifying an optical signal in which a plurality of wavelengths are multiplexed.